Water Heater Leaks Only When a Hot Water Tap Is On

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skeezix

skeezix

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The area underneath my water heater is usually dry. When I take a shower or run the dishwasher or turn a hot water tap on and then check the area, one or two ounces of water are there. If I dry the area and then do not use any hot water, the area remains dry until the next time I use hot water. I cannot locate the source of the leak, but I found that the water inlet union is pretty corroded with white stuff and it is damp.

The pressure inside the water tank is always under house pressure, so why doesn't the water ever leak when all the hot water taps are off???

(I've ordered a new heater. In the meantime I placed a pan underneath the existing heater.)
 
When the heater burner is running, the tank is expanding and changing shape.

So a small split or rust out in the tank, or in the flue pipe going up the center, can gradually open up while everything is extra hot.

So if all your connections are checked and dry, which you can do by sitting there watching while someone runs a shower or whatever, then it seems time for a new water heater.

They are usually good for about 8 to 15 years, but can quit early or last decades, you never know.
 
skeezix said:
The area underneath my water heater is usually dry. When I take a shower or run the dishwasher or turn a hot water tap on and then check the area, one or two ounces of water are there. If I dry the area and then do not use any hot water, the area remains dry until the next time I use hot water. I cannot locate the source of the leak, but I found that the water inlet union is pretty corroded with white stuff and it is damp.
Have you checked the watdr pfessure at rest and while in use there are gauges you can put on a hose connection (launndry) or outside spilot
The pressure inside the water tank is always under house pressure, so why doesn't the water ever leak when all the hot water taps are off???

(I've ordered a new heater. In the meantime I placed a pan underneath the existing heater.)
Click to expand...
 
1. The old heater is 12 years old just like it's warranty.
2. The temperature is set to maximum as it has been for the last several years.
3. I think the union is beyond repair. That and the heater's age point to a heater replacement.
4. The T&P valve has never opened and does not leak.

>So a small split or rust out in the tank, or in the flue pipe going up the center, can gradually open up while everything is extra hot.<

Sounds reasonable to me. That must be what's going on.
 
Upon additional inspection:
While the better half was taking a shower I took a look at the inflow joint to the tank. I found that as long as hot water was running in the house a leak occurred at the point where the copper pipe entered the top of the union. Of course the leak was pretty slow. I can't tighten anything because the entire area is corroded (not shown in the photo below):

water heater union leak.jpg
​
So the question is why doesn't the water leak all the time and not just when a hot water tap is open???
 
The answer to your question MAY have something to do with the slight temperature change.
Or it could be pressure related, even though the pressure would be less while being used.
But in any case, the actual reason doesn't really matter.
 
You should be able to replace that dielectric union.

If you are not skilled at soldering, you could use Sharkbite fittings.

Water might actually be running down from above, like from the cold supply shutoff valve, and you are just seeing it pool up at the plastic part.

Or, incoming cold water is making the union change shape slightly and causing a slight leak.

Meanwhile, I don’t see much corrosion, so tightening might fix it.
Or it might get worse, if ready to fall apart.

Or, you could partially drain the heater after turning off all house water, cold inlet, and turning off the heater.
Unscrew the big brass nut and get a thin layer of teflon pipe dope into everything inside that union, then re-assemble.

Or forget about it, new heater is coming anyway.
I vote for that!
 
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